1. Field of the Invention
The present invention relates to a bearing ring with a low sliding friction for an optical disk which is held for rotation in a cartridge.
2. Description of the Prior Art
Optical disks on which information is recorded and from which information is reproduced with a laser beam have been widely used. These disks include digital audio disks, i.e., so-called compact disks, and optical video disks for recording video signals and audio signals, i.e., so-called laser disks. Because optical disks have capabilities for storing enormous quantities of information and for facilitating information retrieval, they are used for external memories for computers. Magneto-optical disks, writable optical disks and erasable optical disks have been developed for use in information management.
The magneto-optical disk, which is expected to be used as a storage device for a computer, is among those optical disks which, in particular, must ensure high recording and reproducing reliability. To prevent the surface of the optical disk from being damaged and becoming dusty during storage of the optical disk and to prevent the surface of the optical disk from being stained with finger prints and the like during loading of the optical disk on a disk drive, the optical disk is mounted for rotation in a disk cartridge which is made of plastic.
In such a disk cartridge, the cartridge is provided with disk supporting ribs protruding from an inner surface at positions corresponding to the central non-recording area of the optical disk. To prevent damaging the recording area of the optical disk by frictional contact between the recording area of the optical disk and the inner surface of the cartridge, the optical disk is held between the disk supporting ribs so that the recording area of the optical disk will not be in contact with the inner surface of the cartridge. If the optical disk is in direct contact with the disk supporting rib or ribs, the optical disk and the disk supporting rib or ribs will chafe each other to produce dust when the optical disk is rotated. It is, thus, possible that this dust will adversely affect the reliability of the recording and reproducing performance of the optical disk. Therefore, a slippery bearing ring formed by cutting a PET (polyethylene terephthalate) film is interposed between each disk supporting rib and the corresponding portion of the optical disk to prevent the direct frictional contact between the disk supporting ribs and the optical disk. However, the sliding performance of this bearing ring formed by cutting a PET film is not necessarily fully satisfactory and, under severe operating conditions, in particular, the surface of the bearing rings may be abraded to produce dust.
A bearing ring capable of improved sliding performance formed by cutting a film of polyethylene having a very high molecular weight has been tested. The slippery sliding or bearing ring formed of the polyethylene having a very high molecular weight is difficult to handle, due to a lack of firmness, and, hence, it is difficult to correctly apply the bearing ring in place on the optical disk and the bearing ring is liable to deviate from the correct position.